1. Field of the Invention
This invention relates to water filters and, more particularly, to filters for conditioning the water in fish tanks and aquariums.
2. Description of Related Art
In order to maintain the ecological balance of an aquarium, it is necessary to keep the water in the aquarium tank clean and to distribute a supply of oxygen throughout the aquarium water volume. For this purpose, an aquarium filter may be used that pumps water from the aquarium tank, passes the water through a filter medium, and returns the filtered water to the aquarium tank. The filter medium may be selected to remove fish waste products and other particulates, and to adsorb noxious dissolved gases and toxic chemicals from the aquarium water. In this way, a healthy environment for the fish may be maintained and the oxygen supply may be replenished.
A tank-type aquarium filter typically consists of a filter box that accepts a filter cartridge containing the filter medium. The filter draws in water from the aquarium tank through an intake tube by means of an impeller assembly, or pump, and discharges the water into an intake reservoir on the upstream side of the filter cartridge. The water passes from the intake reservoir through the filter cartridge, into a filter discharge reservoir, and over a discharge lip back into the aquarium tank. Many filter designs utilize a generally rectangular, planar filter cartridge. The internal volume of the filter box is roughly divided in half by the filter cartridge, defining the intake reservoir and discharge reservoir. This provides maximum space efficiency and very compact filter dimensions. The filter often includes a lid or cover to keep dust and dirt out of the intake reservoir and discharge reservoir.
As the aquarium water passes through the filter cartridge, the various particulates trapped by the cartridge and any growth thereon gradually slow or block the passage of water through the cartridge. When this happens, the water backs up on the upstream side of the filter cartridge in the intake reservoir. That is, the flow rate of water through the filter cartridge is less than the flow rate of water through the filter pump. As the water level in the intake reservoir rises, the water eventually flows over the top edge of the filter cartridge without being filtered, passing into the discharge reservoir, over the discharge lip, and back into the aquarium tank. As the filter becomes more and more plugged, eventually most of the return waterflow into the aquarium is unfiltered. In order to restore the normal flow of water and the filtration action, the filter cartridge must be changed. Thus, it is necessary for the aquarium user to periodically remove the filter lid to check the condition of the filter cartridge.
Another type of aquarium filter, shown in FIG. 1, incorporates a filter box in which the impeller assembly is removed from its position adjacent the filter cartridge and instead is placed off to one side of it. This allows an overflow window to be positioned next to the discharge lip. The top edge of the overflow window communicates with the intake reservoir. The filter box is constructed so that water ordinarily passes into the intake reservoir, through the filter cartridge, into the discharge reservoir, and over the discharge lip into the aquarium tank. As the filter cartridge becomes plugged, the aquarium water backs up in the intake reservoir. As this happens, the water flow over the discharge lip decreases and the water level in the intake reservoir becomes high enough that water flows over the top edge of the overflow window and into the aquarium tank. That is, the water flows directly from the intake reservoir, down the overflow window, and back into the tank.
In this way, glancing at the aquarium filter to check for water flowing from the overflow window makes the condition of the filter cartridge immediately apparent. Unlike the previously mentioned design, the filter with overflow window allows checking of filter cartridge condition without removing the filter lid. Unfortunately, this configuration does not make maximum use of space. As a result, the filter is larger and more bulky than the non-overflow window type. Thus, the overflow window type filter requires more space for the aquarium installation. A more compact design would be more attractive and could be used in more installations. The configuration without an overflow window is compact and efficient, but is less convenient for filter cartridge upkeep.